Detonable explosive containing dissolved fluorescer

ABSTRACT

TO INDICATE THE PRESENCE OF A LEAKING OR EXUDATING EXPLOSIVE COMPOSITION, A FLUORESCER IS INCLUDED IN THE COMPOSITION WHICH FLUORESCES WHEN EXCITED AS BY ULTRAVIOLET LIGHT. A CLASS OF FLUORESCERS HAS BEEN FOUND THAT IS ESPECIALLY SUITED FOR USE WITH DETONABLE EXPLOSIVES FOR THIS PURPOSE. SUCH FLUORESCERS ARE AROMATIC-BASED COMPOUNDS AND ESPECIALLY PHENYLETHYNYL-SUBSTITUTED AROMATIC COMPOUNDS. THESE FLUORESCERS ARE CHEMICALLY INACTIVE WITH RESPECT TO THE EXPLOSIVE COMPOSITION AND SUBSTANTIALLY OXIDATION-RESISTANT AND STABLE UNDER CONDITIONS OF STORAGE FOR THE EXPLOSIVE COMPOSITION OVER EXTENDED PERIODS OF TIME. THE FLUORESCERS, HOWEVER, MUST BE DISSOLVED IN ORDER TO FLUORESCE WELL WHEN EXCITED. THE SOLVENT FOR THE FLUORESCERS IS ALSO OXIDATION-RESISTANT AND HAS A SUFFICIENTLY LOW VAPOR PRESSURE AT ROOM TEMPERATURES TO RESIST APPRECIABLE EVAPORATION SO AS TO MAINTAIN THE SOLVENCY OF THE FLUORESCERS. THE EXPLOSIVE COMPOSITION MAY BE EITHER POWDER OR LIQUID, BUT A LIQUID FORM IS PREFERRED SINCE THE EXPLOSIVE THEN PROVIDES ITS OWN SOLVATING ACTION ON THE FLUORESCER AND AN ADDITIONAL LIQUID FOR THIS PURPOSE IS NOT NEEDED.

United States Patent Int. Cl. C06b 19/00 US. Cl. 149-2 12 Claims ABSTRACT OF THE DISCLOSURE To indicate the presence of a leaking or exudating explosive composition, a fluorescer is included in the composition which fluoresces when excited as by ultraviolet light. A class of fluorescers has been found that is especially suited for use with detonable explosives for this purpose. Such fluorescers are aromatic-based compounds and especially phenylethynyl-substituted aromatic compounds. These fluorescers are chemically inactive with respect to the explosive composition and substantially oxidation-resistant and stable under conditions of storage for the explosive composition over extended periods of time. The fluorescers, however, must be dissolved in order to fluoresce well when excited. The solvent for the fluorescers is also oxidation-resistant and has a sufficiently low vapor pressure at room temperatures to resist appreciable evaporation so as to maintain the solvency of the fiuorescers. The explosive composition may be either powder or liquid, but a liquid form is preferred since the explosive then provides its own solvating action on the fluorescer and an additional liquid for this purpose is not needed.

BACKGROUND OF THE INVENTION It is common practice to package explosive compositions, such as nitroglycerin, in cartridges or other containers which are then stored in ammunition centers, magazines, or the like. In some instances, the time of storage may extend for an extended period of time, for example, a year or more. In time stored explosives tend to leak or exude the explosive component, especially if it is a liquid. Leakage may be caused by the pressure of stacked containers or cartridges on the lowermost containers. Or relatively high ambient temperatures can sufficiently pressurize cartridges to cause the explosive to exude. Or Water may seep into the cartridges and replace an explosive liquid which then exudes from the cartridge. Still other conditions can cause leakage or exudation of the explosive composition.

A leakage of an explosive composition as from an ammunitiou magazine or dump is not always readily apparent. When the leak is discovered, the actual source of the leak is often difficult to locate precisely. Rather than sort through a supply of explosive materials, endangered by a known leak, the practice has been to destroy the entire supply of explosives in the area by known means. This practice is obviously hazardous and economically wasteful.

It would, therefore, be advantageous if leakage or exudation of an explosive composition could be early detected and, further, if the exact source of the leak could be readily pinpointed. Only that cartridge or other package which suifers the leak need then be isolated and destroyed, thereby reducing the hazard as well as avoiding the destruction of undamaged cartridges.

Dyes are not satisfactory for use with explosive compositions as a means of identifying leaks, because a relatively large amount of leakage must occur before the dye is readily detected. For example, in the case of a liquid explosive, a sheet or layer of substantial area ice and thickness is normally first required for the dye to be visibly discernible. It is obviously important to detect leakage of explosive compositions as soon as possible.

SUMMARY OF THE INVENTION In accordance with the present invention, fluorescers are incorporated with a detonable explosive composition. Only extremely minute amounts of the fiuorescing materials are required to be detectable when subjected to exciting radiation, such as ultraviolet light. However, not all fluorescers are useful in the sensitive environment of detonable explosives of which the chemical stability must not be disturbed for obvious reasons. It is conceivable that some fiuorescers can catalyze unwanted reactions under certain conditions, for example, by catalyzing a chemical reaction or by entering into side reactions which in time deteriorate the explosive material or, worse, precipitate a detonation. Indeed, a chemical change in a fluorescer itself may render the fluorescer less useful or of no use as by shifting the wave length of its emission to a less desirable range, such as one less readily visible to the human eye.

The fluorescers of the present invention are chemically inactive with respect to the explosive composition, the surrounding atmosphere, and the decomposition products of the explosive. The fluorescers must be substantially oxidation-resistant and stable under conditions of storage for the composition over extended periods of time. As used here and in the claims, the phrase extended periods of time is taken to mean at least one year. In general, aromatic-based fluorescing compounds may be used, but phenylethynyl-substituted aromatic compounds are especially useful. A desired class of fiuorescers comprises phenylethynyl-substituted aromatic acene compounds. The preferred fiuorescer is 9,10-bisphenylethynyl) anthracene.

The present fluorescers must be solubilized in order to fluoresce well when excited. If the explosive composition is a liquid, the explosive itself dissolves the fluorescer. If the explosive composition is a solid such as a powder, a solvent must be included to solubilize the fluorescer. In this embodiment, the solvent must also meet the chemical criteria of the fluorescer. That is, the solvent must also be chemically inactive with respect to the explosive composition and substantially oxidation-resistant and stable under conditions of storage for the composition over extended periods of time. Further, the solvent must have a sufiiciently low vapor pressure at room temperatures to resist appreciable evaporation in order to continue the solubilization of the fluorescer. The preferred slovents, when needed, comprise the dialkyl phthalate esters having alkyl groups from one to about eight carbon atoms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The detonable explosive compositions do not themselves form a critical part of the present invention and may comprise those known in the art, whether of solid or liquid form. Solid explosive compositions which may be used are usually powdered and include:

Trinitro-toluene Dinitro-toluene Pentaerythritol tetranitrate Cyclotrimethylene trinitramine Cyclotetramethylene tetranitramine Trinitrophenyl methyl nitramine However, detonable liquid explosives are preferred, since it is easier to distribute a fluorescer more nearly uniformly and completely throughout the explosive. There is no opportunity for segregation of a fluorescer as there may be in the case of an explosive powder. Detonable liquid nitrate esters are preferred although other liquid explosives can be used. Examples of useful detonable liquid explosive compositions include:

Nitroglycerin Ethylene glycol dinitrate Diethylene glycol dinitrate Glyceryl dinitrate Propylene glycol dinitrate Nitromethane Where isomers of these explosives exist, they may also be used as well as mixtures of any of the explosives where compatible. As used here and in the claims, the term detonable explosive composition is taken to include the combination of any detonable explosive composition with a base material such as sawdust, charcoal, diatomaceous earth, nitrocellulose, sugars, and the like; and with conventional additives, where required or desired, such as oxidizing agents, agents to retard deterioration, sensitizers, etc. The quoted term also includes explosive propellants useful in jet or rocket propulsion.

As a general class, aromatic-based fiuorescers meeting the chemical criteria, supra, with respect to a detonable explosive are contemplated. Examples of these are:

9,10 diphenyl anthracene Rubrene 3,9 dibenzoyl perylene 3,4 dibenzoyl perylene 3 ,9 bis (phenylacetyl perylene 2-(2-oxo-2H-1-benzopyran-3-yl)-naphth[1,2-d]oxazole Rubicene IZ-phthaloperinone 2,5-diphenylfuran Violanthrone However, unexpected superiority has been found in a class of aromatic-based fiuorescers comprising the phenylethynyl-substituted aromatic compounds. These fluorescers and a process for preparing them are disclosed, although in another environment, in US. Pat. 3,557,233 to Zweig et al. which is hereby incorporated by reference. Examples of aromatic hydrocarbons in which a phenyl ethynyl group may be substituted include naphthalene, phenanthrene, benzanthracene, chrysene, pyrene, perylene, benzpyrenes, and the like. The phenylethynyl-substituted aromatic hydrocarbons may also themselves be substituted with such other substituents as hydroxy, alkoxy, halo, dialkylamino, diarylamino, alkyl, aryl, cyano, nitro, etc. These groups may be substituted directly on the parent aromatic hydrocarbon or on the phenyl moiety of the phenylethynyl group. Specific structural formulas of certain phenylethynyl-substituted aromatic compounds are given in the cited US. Pat. 3,557,233.

The preferred class of aromatic-based fiuorescers comprises the phenylethynyl-substituted aromatic acene compounds. Among specific compounds of this class are the following of which the first is preferred:

9, 1 O-bis (phenylethynyl) anthracene 5,12-bis (phenylethynyl naphthacene 6, l 3-bis (phenylethynyl pentacene These compounds may also be used in substituted form with such substituents as the alkyl, chlorine, fluorine, carboxy, alkoxy, aryloxy, and aryl substituents, the alkyl and alkoxy substituents containing from about one to about eight carbon atoms, and the aryloxy and aryl substituents containing from about six to about 12 carbon atoms.

The substitution of phenylethynyl groups greatly enhances aromatic-based fiuorescers for use in combination with a detonable explosive composition as herein contemplated. The phenylethynyl groups increase the fluorescing efiiciency of the resulting compounds. Substitution of phenylethynyl groups on aromatic fiuorescers provides significant shifts in emitting wave lengths to longer wave lengths which are nearer the optimum of human visual sensitivity. The resulting compounds are more strongly fluorescent and glow with a green color which is easily seen even in the dark under ultraviolet radiation.

In spite of the presence of the triple unsaturation of the ethynyl moiety, the fiuorescers are quite stable as used herein. Further, these fiuorescers are sufficiently soluble in known liquid explosives and can be solubilized, as required, in this manner as hereinafter more fully described. Nothing has been found which approaches the efficacy of the phenylethynyl-substituted aromatic acene compounds in this environment and especially 9,l10-biS (phenylethynyl anthracene.

The present fiuorescers must be solubilized in order to exhibit these salutary properties. Where the detonable explosive composition is a powder, a solvent is used which like the fluorescer must be chemically inactive with respect to the explosive composition and substantially oxidation-resistant and stable under conditions of storage of the composition over extended periods of time, for example, a year or more. Water cannot be used as a solvent because at least the preferred fiuorescers are not sufiiciently soluble in water. Furthermore, water tends to hydrolyze materials present. The solvent must, therefore, be organic and have a sufficiently low vapor pressure at room temperatures (about 65 F. to about F.) to resist appreciable evaporation which otherwise would cause deposition of the fluorescer as a solid, that is, in a non-solvated form. Preferably, the solvent for use with a powder explosive has a boiling point of at least about 200 C. at standard condtions. In general, the plasticizers used in the synthetic resin industry which meet this temperature requirement can be employed. Examples of specific useful solvents include triethyl phosphate, tricresyl phosphate, dibutyl Cellosolve, Carbitol, butyl Carbitol, dibutyl Carbitol, diethylene glycol, ethylene glycol, and the like. A preferred class of solvents comprises the dialkyl phthalate esters having alkyl groups from about one to about eight carbon atoms, such as dimethyl phthalate, dibutyl phthalate, etc. The alkyl groups need not be the same.

When the detonable explosive composition is a liquid, such as any of those previously mentioned, the liquid itself serves as the solvent, and no additional solvent need be added.

Whether a liquid explosive or a solvent like a dialkyl phthalate is used to dissolve the fluorescer, only a suflicient amount of the fluorescer need be present to be visibly discernible when subjected to exciting radiation. Normally this is accomplished by an amount of the fluorescer which provides at least a 10- molar solution with Whatever solvent is used, although fluorescent solutions as strong as 5 molar can be used. More fluorescer is only wasteful. A preferred molar range of a fluorescer in the solvent is from about 10- to 10- molar concentration. One convenient manner of solubilizing a fluorescer in a solvent is merely to allow the solvent to drain through a small bed of the fluorescer.

In practice, in the case of a powder explosive composition, the fluorescer is dissolved in a solvent and the resulting solution then admixed with the powder having a particle size Within a conventional range of particle sizes for explosives. This disperses the fluorescent and solvent substantially throughout the explosive composition. In the case of a liquid explosive, the solution of the fluorescer is made directly into the liquid which uniformly disperses the fluorescer throughout the explosive. In either case, the explosive composition is then conveniently packaged as may be desired. After the packages, such as cartridges, are stacked in an ammunition magazine or the like, the area may be periodically checked by bathing the packages with ultraviolet radiation. If a leak or exudation has occurred, the seeping explosive carries with it some of the fluorescer which is readily detectable. Further, the exact source of the leak is easily determined by tracing the route of the fluorescing material back to its beginning.

The following examples are intended only to illustrate the invention and should not be construed as limiting the claims.

Example 1 This example illustrates the formation of a fluorescent liquid explosive. An amount of 0.002 gram of 9,10-bis- (phenylethynyl)anthracene, which is a solid crystalline material, was suspended in 20 grams of nitromethane, a liquid explosive, for 48 hours at 70 F. Approximately 10 percent of the 9,l-bis(phenylethynyl)anthracene dissolved in the nitromethane yielding a solution containing approximately 0.001 weight percent of the anthracene (approximately a 3 X '5 molar concentration).

The resulting solution displayed an intense green fluorescenc e when radiated with a standard ultraviolet lamp. In fact, the same solution was also found to be fluorescent under daylight exposure. The solution could be packaged in any of the known conventional packages such as cartridges for liquid explosives.

Example 2 This example illustrates the formation of a fluorescent explosive powder and also the need for solubilizing the fluorescer. Smokeless powder was used, purchased under the trademark Bullseye Brand, consisting of liquid nitroglycerin and solid nitrocellulose combined in a known manner to produce a gel. An amount of 1 gram of the smokeless powder was mixed with 2 grams of acetone and 0.001 gram of 9,10bis(phenylethylnyl)anthracene. While the mixture was still heterogenous, a spatula was quickly thrust into the mixture and withdrawn. The acetone had caused the nitroglycerin to exude from some of the gel formed with the nitrocellulose. After evaporation of the acetone, the withdrawn specimen of the mixture was found to display an intense green fluoroescence when radiated with a standard ultraviolet lamp. Even though the acetone had evaporated, the anthracene compound was dissolved in the exuding liquid nitroglycerin.

After two hours, the mixture was found to be substantially homogenous. The nitroglycerin and nitrocellulose were conventionally combined to form a gel with little or no free liquid nitroglycerin. When a spatula was thrust into the mixture and a specimen withdrawn, followed by evaporation of any acetone present, the specimen would not fluoresce when radiated with ultraviolet radiation. In the absence of either a liquid nitroglycerin or the acetone, the 9,10-bis(phenylethylnyl)anthracene would not fluoresce because it was not in a dissolved state.

The mixture of this example could be used as a propellant for rocket propulsion as used in military ordnance.

In place of 9,10-bis (phenylethynyl)anthracene, any of the other phenylethylnyl-substituted aromatic compounds disclosed could have been used in either example.

The use of fluorescers in explosive compositions has several additional advantages. Explosive compositions are well known to be toxic. Workers handling such materials must follow a rigid hygienic regimen. After washing, workers handling the present explosive compositions can expose parts of their bodies to ultraviolet radiation and determine if all of the explosive material has been washed way by the absence or presence of fluorescing. Similarly, residual, non-exploded portions of explosives in bore holes made for rock blasting or the like can be hazardous. After using explosives of the present invention, the blasting site can be exposed to ultraviolet radiation to determine if any unexploded explosive remains. The present invention can also be used as a means of quality control in the manufacture of an explosive composition by observing the composition under ultraviolet radiation and noting if a fluorescer is suificiently uniformly distributed throughout an explosive. If a fluorescer is satisfactorily distributed, it indicates the explosive is also sutficiently homogenously distributed as throughout an adsorbing medium.

While the foregoing describes several preferred embodiments of the present invention, it is understood that the invention can be practiced in still other forms within the scope of the following claims.

I claim:

1. A detonable explosive composition which comprises a compound having at least one nitro group and containing a fluorescer comprising phenylethynyl-substituted aromatic compound, said fluorescer being dissolved in an organic solvent and present in sufficient amount to be visibly discernible when subjected to exciting radiation, said fluorescer and solvent being dispersed substantially throughout said explosive composition, said fluorescer being chemically inactive with respect to said composition and substantially oxidation-resistant and stable under conditions of storage for said composition over extended periods of time, and said solvent being chemically inactive with respect to said composition, oxidation-resistant, and having a sufliciently low vapor pressure at room temperatures to resist appreciable evaporation.

2. The explosive composition of claim 1 in which said composition is in powder form, and said dissolved fluorescer and solvent are dispersed substantially throughout said powder.

3. The explosive composition of claim 1 in which said explosive composition is in liquid form and defines said solvent in which the fluorescer is dissolved.

4. The explosive composition of claim 1 in which said explosive composition is a liquid nitrate ester and defines said solvent in which the fluorescer is dissolved.

5. The explosive composition of claim 1 in which said fluorescer is a phenylethynyl-substituted aromatic acene compound.

6. The explosive composition of claim 1 in which said fluorescer is a phenylethynyl-substituted acene aromatic compound selected from the group consisting of 9,10-bis- (phenylethynyl) anthracene; 5,12 bis(phenylethynyl) naphthacene; and 6, 13-bis (phenylethynyl pentacene.

7. The explosive composition of claim 1 in which said fluorescer is 9,l0-bis(phenylethynyl)anthracene.

8. The explosive composition of claim 1 in which said fluorescer is selected from the group consisting of 9,10-bis- (phenylethylnyl)anthracene, and the alkyl, chlorine, fluorine, carboxy, alkoxy, aryloxy, and aryl substituents thereof, the alkyl and alkoxy substituents containing from about one to about eight carbon atoms, and the aryloxy and aryl substituents containing from about six to about 12 carbon atoms.

9. The explosive composition of claim 1 in which said organic solvent is a non-fugitive solvent having a boiling point of at least about 200 C. at standard conditions.

10. The explosive composition of claim 1 in which said solvent is a dialkyl phthalate ester having alkyl groups from one to about eight carbon atoms.

11. The explosive composition of claim 1 in which said fluorescer is present in an amount at least to provide a 10" molar solution with said solvent.

12. A packaged explosive containing the explosive composition of claim 1 from which said composition is subject to leakage or exudation.

References Cited UNITED STATES PATENTS 3,474,730 10/1969 Sheeran 1492 X 3,590,003 6/1971 Meyers et a1. 14914 X STEPHEN I. LECHERT, IR., Primary Examiner US. Cl. X.R. 

